It is possible that the setup page does not use https and is not secured. Your browser should have an advanced option to continue anyway.
Another possibility is that the site might be trying to redirect and the browser bocks it. When this happened to me the old Internet Explorer browser was the only one that would work.
I tried Internet Explorer but it also said it was not secure. It says it is not secure when logged into my comcast account. I only have an ethernet connected desktop, with network set to Private. Should I really be worried it says Not Secure?
Chrome should just say "not secure".
Is that IP address correct. Usually it's 192.168.100.1
It's 10.0.0.1 for the Comcast supplied gateway devices...
I think for https to be secure, the server needs a certificate, but I don't think certificate issuers issue them to devices with local ip addresses. ? So, you get only an http connection, and browsers have been making more of a point lately of pointing that out but saying things like "not secure".
I guess you only need to worry if you have snoops on your own LAN.